Doubts persist on the natural history of the virus and further studies are needed to identify the exact reservoir of the monkeypox virus and how it is maintained in nature.

对该病毒的自然史仍存有疑问，需要进一步继续研究，以确定猴痘病毒的确切贮主，以及该病毒在自然界是如何生存下来的。

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The exact association between smoking and back pain will have to be clarified in appropriate studies.

吸烟与腰背痛之间确切的关系应该由恰当的研究以澄清。

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Many studies have shown that the incidence of the disease is a complex mechanism, multiple factors involved in the pathophysiological process, but the exact pathogenesis is not clear.

许多研究表明，该病的发病机制是一个复杂、多因素参与的病理生理过程，但确切的发病机制并不明了。

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"Traffic forecasting is not an exact science, " agrees Michael Demetsky, head of the Center for Transportation Studies in Charlottesville, Va.

NPR: Bumper to Bumper: Predicting Traffic Flow

To investigate the exact nature and impact of these changes, UNESCO is launching two studies on the relationship between environmental degradation and migration in the Sahel.

UNESCO: OFFICE IN DAKAR